I was changing out the spark plugs on the 65chevelle because they looked suspicius and I did not buy them. The plugs that were on the car were Accel U grove plugs you get at Pep Boys. The orginal owner must have asked for them cause they gave him regular SBC plugs. The sprak plugs needed for aluminum edelbrock heads or any good head is flat washer style. 750 by 3/4 reach so I picked up some Champion RY12YC plugs. The Accels were tappered and only had a 1/2 reach. Well will see if it makes a difference. Dont trust those counter guys, do your home work first.